Historically, power system protective relays, in particular electromechanical relays, only provided an indication of whether or not they had operated to produce a trip (opening) of an associated circuit breaker. Usually this information was provided via a light or a colored "drop panel", on the front of the relay, known as a target. These targets were usually reset manually. Sometimes, on very important power lines, utilities installed sequence-of-event reporting (SER) equipment and/or oscillographs. This was done to determine whether a particular relay's trip operation (when it occurred) was in fact correct. However, such equipment, which is independent of the individual relays, typically produced a substantial amount of data, which required well-trained personnel substantial time to analyze and to reach a conclusion concerning proper operation of the device. Delays in evaluating the data and the experience of the analysts, however, made sequence-of-event reporting analysis somewhat problematic. Additionally, the analog data measured and reported by an oscillograph might not be the same data measured and utilized by the protective relay in reaching its trip decision.
Without such additional equipment, however, proper operation of the relays was difficult, if not impossible, to determine. With simple "target" indications, for instance, it was not even possible for the operator to be sure that a lit target was from the most recent trip of the relay. The SER/oscillograph equipment itself, however, had inherent disadvantages of high cost of purchase, installation and maintenance. Additionally, wiring to an SER from several independent relays could result in a failure of a portion or all of the protection system in the event of a failure of an input to the SER.
With the development of digital (microprocessor based) relays, however, information could be readily produced from the relay apparatus itself concerning the status of various aspects of the relay at selected times, notably at the time of generating a trip signal for an associated breaker. This has become known as "event reporting". Event reports typically set forth with significant particularity the input voltages and currents to the relay, go/no-go status of the various relay elements, the various element settings and the contact I/O status during the times of disturbances within the power system, all as a function of time. Thus, detailed information on the operation of the relay was and is now available to the user without the installation of special additional equipment, such as the SERs and oscillographs described above.
The information provided by an event report will typically span in time the pre-fault, fault and post-fault conditions of the power system, so that the performance of the relay elements, as well as the value/condition of the voltages and currents on the power line and the relay input and output contacts, can be seen throughout the event. The information which is available from the event report is quite significant. At least some of the information available from event reports would not be obtainable even from known separate equipment. Examples of such information include fault location, relay target status, fault duration (as measured by the relay) and the actual analog input quantities available to the relay. The status of many internal elements of the relay, relative to the analog inputs, with respect to time, are also reported. Such information is not available through external separate equipment such as SERs. The status of certain internal elements of the relay can in some cases be ascertained with output contacts and programming the relay elements to the output contacts. However, this approach is expensive and requires knowledge of any regular delay in the operation of the output contacts.
SER devices are still used, however, on some power lines, in addition to protective relays which produce the above-described event reports. Such an arrangement, of course, results in a large amount of data. The more data, however, the more difficult and the longer it takes to thoroughly and correctly analyze it. A current trend is to store more and more information, with higher and higher resolution. This trend, fueled in part by lower processing and memory costs, creates more data than can be practically examined by an analyst and thus actually hinders performance analysis, even though it is believed that the additional information will assist the analyst in evaluating proper protection system operation.
Some relays store many seconds worth of 64 samples per cycle data around each event. This data must be downloaded from the relay to a computer and interpreted by an experienced analyst to evaluate a particular relay operation relative to the event. All of this analysis, of course, takes a considerable amount of time, even for trained analysts, to perform. The likelihood of obtaining fast conclusions from such large amounts of data is relatively unlikely and only will worsen with more data.
In addition, it is often the case that several relays in a protection system will produce event reports for the same event. For instance, it is easily possible that a single fault will have an effect on as many as twelve or even more line terminals. If each line terminal has at least one protective relay with data storage and event reporting capability, it can be readily seen that the analytic requirements quickly become very high. With this large amount of data available to be analyzed, it is common for analysts to evaluate only the most likely relays for possible misoperation. This leads to missed opportunities for correction of unknown system shortcomings, which if corrected in time would avoid future misoperations.
Even with the additional data being collected, there are some relay operations which require such a long time to complete, that the data showing the entire operation of the relay simply cannot be reasonably collected and analyzed. For instance, 15 seconds of recorded data for an event is an exceedingly long time. This could be as much as 57,600 rows of data for just one relay. With multiple relays responding to a fault, the data becomes overwhelming. The large amount of data may ironically result in a delay or even a complete miss of particular problems in the system.
Yet, some elements have an operating time substantially in excess of 15 seconds. Some time overcurrent elements, for instance, have an operating time of over 100 seconds. Hence, even a relatively long 15-second data collection period would still not be adequate to evaluate the performance of such relay elements.
Another difficulty with large amounts of data collected is the storage capacity which must be available in the relay. This adds significant cost to the apparatus, which is eventually passed on to the ultimate purchaser thereof.
Hence, even though protective relays now have the capability of accumulating a large amount of potentially important data relative to a system event, information concerning the actual performance of the relay requires a detailed analysis of all that data, which still may be incomplete relative to a true picture of relay operation. Further, promptness of the data analysis frequently becomes an issue, due to lack of experienced personnel, the increasing volume of the data collected and/or adequate time of the personnel. Thus, data may be available (even though incomplete), but nothing really useful results. Important information about the overall quality of the protection system in effect remains hidden in the large volume of data which is collected but not effectively analyzed.
A system is needed to provide accurate information on protection quality/performance rather than just raw data. Further, such a system should be able to communicate the conclusions to those who have the operational responsibility for the system.